sudokUI › Sudoku techniques › Hidden Triple
Hidden Triple in sudoku
flip side of a naked subset · in a line: Swordfish sideways · how it fits
Three digits, all still missing from a unit, whose places in that unit fall within the same three cells, though a digit need not appear in all three.
Why it works
The unit needs all three digits in three different cells, and only these three cells can take them, so the digits fill all three cells. Remove all candidates except those three digits from the three cells.
How to spot it
For each missing digit in a unit, list its possible cells, then look for three digits whose lists together name only three cells.
Worked example
Hidden Triple: in row 8, digits 3/5/9 fit only in r8c4, r8c6, r8c9, so all other candidates there can be removed.
Practise it on a real puzzle. sudokUI generates a puzzle that needs Hidden Triple and takes you straight to the position where it applies. Hints draw the pattern on the board and explain the step.
In a puzzle's rating
Each time the solver needs Hidden Triple, the puzzle's difficulty rating grows by 100. Its class is Medium. It is needed in 1 in 110 puzzles that sudokUI generates. How the rating works.
More subsets
Naked Pair · Naked Triple · Hidden Pair · Naked Quadruple · Hidden Quadruple